Saw-toothed wave form generator



Patented July 4, 1939 UNITED STATES PATENT OFFICE SAW-TOOTHED WA VE FORMGENERATOR Application August 11, 1936, Serial No. 95,339 I In GermanyAugust 13, 1935 Claims. (01. 250-36) The invention relates to a circuitarrangement for producing saw-tooth shaped voltage curves fortrapezoidal scanning and the trapezoidal composition of televisionimages. It is possible to 5 produce a line deviation having a variableposition in the course of the duration of a line series, by connectingan amplifier tube having a condenser placed in parallel thereto to aplate voltage source across a resistor, said source not l0 onlyfurnishing a constant voltage, but, in addition, a saw-tooth shapedvoltage having the frequency of the line series alternation. Thedefinition of the line series alternation will be em ployed in thefollowing description with respect 16 to the line skip method. Where atransmission other than that according to this method is considered, thedefinition of the line series alternation is identical with the picturealternation. From the constant voltage source the condenser is at firstcharged across the said resistor with constant current within eachlineduration, and the amplifier tube following the termination of eachline duration is rendered permeable to current, so that the condensercharge disappears across the tube. This circuit arrangement has thefurther advantage that the produced sequence of saw-tooth shaped linevoltages receives an additional saw-tooth shaped component having thefrequency of the line series alternation, since the amplifier tubecannot completely discharge the condenser within each line pause.Therefore, it is necessary at any rate to provide'means by which onlythe desired number of saw-teeth of the line growing within-a duration ofthe line series will be obtained.

The invention relates to a circuit arrangement bywhich the desirednumber of saw-teethof the line can be produced directly withoutsuperimposing a component having the frequencyoi the line series. Tothis end, according to the invention, a multi-grid tube is used asamplifier tube, and a current-free grid of this tube is fed with avoltage which is in equal phase with the saw-tooth shaped component ofthe condenser charging'voltage, and having line series frequency.

An embodiment of the invention is schematically illustrated in Figure 1of the drawing. Fig. 2' is an explanatory curve.

It! designates a hexode whose grid l which blocks the current passageduring the line duration, has positive pulses applied thereto during theline pause. Grid 2 just as grid 4 has a positive potential relative tothe cathode. H is a resistor placed between the positive pole of adirect voltage source, and the anode of the tube,

and I2 designates a blocking condenser across 1 which a saw-tooth shapedvoltage having line series frequency is applied. There is connected inparallel to the hexode, a condenser l3, which is charged across theresistor H, and discharged ii across the tube H]. The grid 3 of the tubeis connected to a voltage divider consisting of resistors i4 and I5, andwhich may contain a blocking condenser Hi.

In its details the circuit arrangement, accordl0 ing to Figure l,operates in the following manner. The voltage effective at point Pcharges the condenser I3 across resistor II as long as the tube It! isblocked, whereby the course of the condenser voltage. followsapproximately an efunction such as shown in Figure 2. It is assumed thatthe condenser may at first have zero charge, and that the chargingbegins at the time zero.

The charge at the condenser then increases 2 at first in a linearfashion, approaching later asymptotically the voltage U active. at pointP, and composed of a direct voltageland a sawtoothvoltage having lineseries frequency. The increase in the voltage at the condenser cor- 25responds to an e-function when assuming the voltage at point P to beconstant within the duration of the line. Since, however, this voltageis variable within the duration of the line although only in a smalldegree, the voltage course 30 at the condenser deviates slightly from anefunction. Notwithstanding this fact, the first partof the voltageincrease at the condenser remains practically linear. During the linepause a positive potential is applied to grid 1 of the 35 hexode, thusrendering the tube permeable to current, at a moment t1 up to whichthere still exists a practically linear voltage increase at thecondenser. The condenser whose voltage has the direction indicated bythe plus and minus 40 signs, will then be discharged across the tube toa value and with a current determined. by the voltage at grid 3 which istapped from the voltage divider l i, I5. This voltage at grid 3 becomesthe more positive, the higher the inciden- 45 tal value of the saw-toothvoltage having line series frequency. Therefore also the charge at thecondenser decreases the more during the pause between lines, the morepositive grid 3.

In Figure 2, the voltage course at condenser 50 I3 during the line pause(titz) is shown as straight line, but actually also this voltage courseis an' e-function in the sense above explained, but which can beconsidered linear during the line interval with sufficient accuracy. Atthe 55 time t2, the current passage through tube It] is again blocked,so that a new discharge of the condenser l3 takes place, but which leadsto a higher condenser voltage within the duration of the line, since nowowing to the increased component of the line series saw-tooth, thecharging voltage of the condenser is higher. The discharge current ofthe condenser which begins at the time its is likewise larger than thatin the moment tub in view of the voltage at grid 3 being higher than inthe moment t1. Consequently, within the line interval, the condenserwill be discharged down to a lower voltage than the voltage reached atthe time Q. In the moment is the current passage through the tube IDwill again be blocked, and thus a new charge of the con denser initiatedand so forth. The maximum value of the condenser voltage at each newcharge is therefore higher within each line series, than at thepreceding charge within the same line series, and the minimum value ofthe condenser Voltage following each discharge is lower than at thetermination of the preceding discharge. Thus at condenser l3 thereappears a sequence of line saw-teeth with increasing amplitude withoutsuperimposition of a component having line series frequency, such as isthe case when using an ordinary amplifier tube for the discharge of thecondenser.

It is especially notable that it is possible to eliminate the saw-toothcomponent having line series frequency without power being required. Thegrid 3 of the hexode has no current and is to be considered as currentfree in the same sense as for instance a negatively biased control gridof an ordinary triode. In the same way the voltage divider l4, l5likewise does not require direct current from the plate current sourceif a block condenser 16 is inserted in the voltage divider circuit asshown in Figure 1. As indicated in this figure, in place of the blockcondenser IS the condenser [2 may also be provided.

We claim:

1. A circuit for producing a current and voltage of modulated sawtoothwave form comprising a vacuum tube having a cathode, a first controlgrid, a second control grid and an anode, a condenser connected in thecathode anode circuit of said tube, a source of potential connected tosaid anode, a resistance connected to said source of positive potential,said resistance, condenser and source of positive potential beingconnected in series, means for applying an external source of regularlyre-occurring impulses to said first control grid to cause the tube tobecome alternately conducting and non-conducting whereby a sawtoothvoltage is developed and means for applying at least a portion of saidvoltage of sawtooth wave form developed within said circuit to saidanode and said second control grid whereby a current and voltage ofmodulated sawtooth wave form will appear across said con denser, thefrequency of said applied voltage of sawtooth wave form beingsubstantially less than the frequency of said applied impulses.

2. A circuit for producing a current and voltage of sawtooth wave formhaving a constant frequency and a modulated amplitude comprising aVacuum tube including a cathode, a first control grid, a second controlgrid and an anode, a condenser connected in the anode-cathode circuit ofsaid tube, a source of potential connected to said anode, a resistanceconnected to said source of positive potential, said resistance,condenser and source of positive potential being connected in series,means for maintaining said second control grid at a potential negativewith respect to the cathode, means for regularly varying the potentialof said first control grid at a frequency materially greater than thefrequency of said voltage of sawtooth Wave form whereby said tube isrendered alternately conducting and non-conducting whereby a sawtoothvoltage is developed, and means for superimposing at least a portion ofsaid sawtooth voltage developed within said circuit upon the anode andthe second control grid of said tube.

3. A circuit for producing modulated sawtooth wave form comprising avacuum tube having a cathOde at least one control grid and an anode, acondenser connected in parallel with the space path of said tube, asource of potential connected to the anode of said tube, a resistanceconnected to said source of positive potential, said resistance,condenser and source of positive potential being connected in series,means for causing said tube to become alternately conducting andnonconducting whereby a sawtooth voltage is developed at a frequency inexcess of the frequency of the said sawtooth wave, and means forsuperimposing at least a portion of said developed sawtooth voltage onto the anode of said tubewhereby a current or voltage of modulatedsawtooth wave form will appear across the condenser.

4. A circuit for producing a current and voltage of modulated sawtoothwave form comprising a vacuum tube having a cathode, at least onecontrol grid, and an anode, a condenser connected in the cathode-anodecircuit of said tube, a source of potential connected to said anode, aresistance, said resistance being serially connected in a series circuitincluding said condenser and said source of potential whereby saidcondenser is charged from said source of potential through saidresistance, means for applying an external source of regularlyre-occurring impulses to a control grid of said tube to cause the tubeto become alternately conducting and nonconducting whereby a sawtoothvoltage is developed, and means for applying at least a portion of saidsawtooth Voltage developed in said circuit to the anode of the tubewhereby a current and voltage of modulated sawtooth wave form willappear across the condenser.

5. A circuit for producing a current and voltage of modulating sawtoothwave form comprising a vacuum tube having an anode, a first controlgrid, a second control grid, and an anode, a condenser connected in thecathode-anode circuit of said tube, a source of energizing potentialconnected to said anode, a resistance, said re sistance, said source ofpotential and said condenser being connected in series, means forapplying an external source of regularly re-occurring impulses to saidfirst'control grid to cause the tube to become alternately conductingand non-conducting, whereby a sawtooth voltage is developed within saidcircuit and means for applying at least a portion of said sawtoothvoltage developed within said circuit of said anode and said secondcontrol grid whereby a current and voltage of modulated sawtooth waveform will appear across said condenser.

RUDOLF URTEL. ROBERT ANDRIEU.

